1. Field Of The Invention
The invention relates generally to the art of gas analysis and, more particularly, is directed to a new metabolic rate analyzer.
2. Description Of The Related Art
All of the processes that take place in the body ultimately result in the production of heat. Heat production and metabolism can be viewed in a similar context. In direct calorimetry heat production is measured directly to provide a measure of metabolic rate or function.
All energy metabolism in the body ultimately depends on the utilization of oxygen. Indirect calorimetry involves measuring the consumption of oxygen (O.sub.2) and the production of carbon dioxide (CO.sub.2) to provide an indirect estimate of energy metabolism. There are many different gas analysis techniques used in the prior art of indirect calorimetry. These gas analysis techniques are used by physicians for clinical reasons, by athletes to measure performance, and by coaches to measure fitness levels.
It has been known for some time that the analysis of a subject's respired air provides valuable information relating to the physical condition of the subject. The four most commonly measured variables are respiratory volume, oxygen consumption, carbon dioxide production, and respiratory exchange ratio (RQ), which is the ratio of carbon dioxide produced to oxygen consumed.
One of the earliest efforts to conduct indirect metabolic rate analysis involved use of a so-called Douglas Bag. A Douglas Bag metabolic analysis technique involved the timed collection of expired breath in a rubberized bag, measuring the volume of expired gas collected, and analyzing the gas composition contained within the rubberized bag for O.sub.2 and CO.sub.2 content. Metabolic rates were then calculated from the data obtained. The Douglas Bag technique was time consuming, subject to error, and could only be performed on relatively stationary subjects in well-equipped laboratories. Also, this technique was not well-suited to the measurement of short-duration transients in metabolic functions.
Since the data obtained from respiratory gas analysis is so valuable in diagnosing cardiopulminary dysfunction and evaluating overall cardiovascular fitness, intense effort has been directed towards the development of simpler, faster, automated metabolic analyzers. The intense interest in physical fitness and aerobic exercise, such as running, as helped to focus further effort in this field. Many instruments are presently available for the determination of the total volume of respired air from a subject being studied. These devices include spirometers, plethysmographs, and pneumotachographs. Numerous instruments are also available for determining O.sub.2 content and CO.sub.2 content in respired gas. Some of the more recent techniques involved the use of a discrete zirconium oxide O.sub.2 sensor and a non-dispersive infrared (NDIR) gas analyzer for determining CO.sub.2 content. While, such instruments are accurate, they are large, heavy, they require frequent calibration, and special operating skills. Normally, such instruments are so large that they are incorporated in a wheeled cart, which is used only in a clinical or laboratory setting.